A fuel assembly included a plurality of fuel rods, fuel spacers for maintaining gaps between the fuel rods and a channel box. The channel box includes spacer support portions projecting inwardly from an inner surface of the channel box and supporting the fuel spacer in a transverse direction and creep deformation inhibition portions disposed at the lower end portion of the channel box and projecting inwardly. The distance between the spacer support portions disposed to oppose one another in a horizontal direction is smaller than the distance between the creep deformation inhibition portions opposing one another in the horizontal direction.